The initiation and control of lymphocyte responses depend on the interaction of T cells with dendritic cells (DCs), a key type of antigen presenting cells (APCs). DCs are a complex innate immune cell population that recognize and respond to pathogen-associated and danger-associated signals. DCs are derived from bone-marrow progenitors and can be found in blood, lymphoid organs, and various tissues. Upon capture and process of pathogen-derived material, DCs present antigens in the context of MHC molecules on the surface of the cell. The interaction between TCR/co-receptor and MHC/peptide complex, and other co-stimulatory molecules presented on the surface of T cells and DCs, respectively, leads to activation and differentiation of naïve T cells.